This project will use spectral karyotyping and whole genome microsatellite analysis to characterize chromosomal aberrations that cannot be characterized by light microscopic techniques. We will accrue patients with derivative chromosomes and abnormal phenotypic features and perform SKY analysis and microsatellite analysis. The protocol is currently closed to further accrual and will be phased out. - pediatric research, mental retardation, genetics, clinical research - Human Subjects